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Abdomen:Solid viscus:Pancreas
The pancreas is a retroperitoneal organ that has both endocrine and exocrine functions: it is involved in the production of hormones (insulin, glucagon and somatostatin), and also involved in digestion by its production and secretion of pancreatic juice (via duct to duodenum) Pancreatic ducts carries pancreatic juice through the gland. In the majority of individuals, the main pancreatic duct empties into the second part of duodenum at the ampula of Vater. It has four parts, head, neck, body and tail. The big head is connected by a short neck to the to the body that crosses the midline and tapers to a narrow tail on the left. *'Head:' Thickest part; lies to the right of superior mesenteric vessels (SMA, SMV) **Left: SMA, SMV. **Posterior: IVC and tunneled by pancreatic portion of CBD. **Anterior: transverse mesocolon. **Attached to "C" loop of duodenum (2nd & 3rd parts) **Uncinate process: Head extension, posterior to SMV and SMA to the left *'Neck: '''narrow band of pancreatic tissue **posterior: splenic vein joins SMV forming portal vein, SMA **inferior: transverse mesocolon *'Body:' triangular shaped, at L1, pass across left renal vein, aorta, left crus, left psoas, left adrenal gland, to hilum of left kidney. **posterior: splenic vein lies in groove on the body **anterior: covered with peritoneum forming the back surface of the omental bursa (lesser sac) **superior: coeliac axis and splenic artery *'Tail:' passes forward to the anterior surface of the left kidney. Accompanied by the splenic artery, vein and lymphatics within the two layers of splenorenal ligament, and reaches the hilum of the spleen. *Pancreatic duct: continuous tube running from the tail to the head, joined by the CBD at 60 degrees at the ampulla of Vater. Blood supply *Arteries to head mainly from gastroduodenal artery **Pancreaticoduodenal arcade of vessels around head also supplied by SMA branches *Arteries to body & tail from splenic artery (dorsal branch, pancreatic magna etc) *The pancreatic and pancreatoduodenal veins drain blood from the pancreas into the portal system. Lymph drainage: lymphatics follow the course of the arteries *To the left of the neck, the pancreas drains into the splenic nodes. *The head drain into the coeliac group *Uncinate process process into superior mesenteric group of preaortic lymph nodes. Nerve supply: *Parasympathetic vagal fibres via posterior vagal tunk and coeliac plexus (exocrine) *Sympathetic from T6-T10 via splanchinic nerves and coeliac plexus (vasoconstrictor) *Pain afferents accompany sympathetic and radiate to thoracic dermatomes 6-10. Variant anatomy Annular pancreas An annular pancreas is an uncommon ( ≈ 1 in 20 000 1) variation with partial or complete surrounding of the duodenum with pancreatic tissue. The ventral pancreatic "anlage" is responsible for this anomaly by dividing early into two segments: * often detected incidentally in asymptomatic patients * may be associated with duodenal stenosis, postbulbar ulcerations, pancreatitis or biliary obstruction Bifid pancreas Rare branching anomaly of the pancreas tail and its duct system, also known as fishtail pancreas. Ectopic pancreatic tissue Ectopic pancreatic tissue refers to pancreatic rests that lie outside and separate to the pancreatic gland. It is reportedly quite common, affecting ~5% (range 1-10%) 1 of people, most of whom are completely asymptomatic. Recognised locations for ectopic pancreatic tissue include stomach, proximal duodenum, ileum and Meckel's diverticulae. The pancreatic ductal embryology is moderately complicated, leading to a number of anatomical variants of the pancreatic ducts. The normal arrangement is for the entire pancreas to be drained via a single duct, to the ampulla of Vater through the sphincter of Oddi. Conventional pancreatic ductal anatomy Main pancreatic duct * portion of the dorsal duct proximal to the dorsal-ventral fusion point * drains at the ampulla of Vater * connects with the duct of Santorini (see below) if present Pancreatic duct of Wirsung * segment of the ventral duct between the dorsal-ventral fusion point and the major papilla * continuous with the main pancreatic duct Accessory pancreatic duct (of Santorini) * portion of the dorsal duct distal to the dorsal-ventral fusion point * drains anterior and superior portion of the head ** in 70% of individuals drains at the minor papilla ** in 30% of individuals persists as a branch of the main pancreatic duct Variant anatomy Variants of the pancreas, which result in ductal variations are covered in the pancreas article. * Pancreas divisum: most common variation of pancreatic duct formation and can account for up to 14%. It results from failure of fusion of dorsal and ventral pancreatic anlages. As a result, the dorsal pancreatic duct drains most of the pancreatic glandular parenchyma via the minor papilla. Possible risk of pancreatitis. Pancreatic divisum can result in a santorinicele, which is a cystic dilatation of the distal dorsal duct, immediately proximal to the minor papilla . ** Three subtypes are known: *** type 1: classic, no connection at all; occurs in the majority of cases (~70%) *** type 2: absent ventral duct, minor papilla drain all of pancreas while major papilla drains bile duct (~25%) *** type 3: functional, filamentous or inadequate connection between dorsal and ventral ducts (~5%) * '''Meandering main pancreatic duct:' comprises of a reverse Z-type and loop-type of pancreatic ducts. * Ansa pancreatica: rare anatomic variation. It is a communication between the main pancreatic duct and the accessory pancreatic duct. * Anomalous pancreaticobiliary junction: anomalous pancreaticobiliary junction refers to the union of the pancreatic duct and common bile duct outside the duodenal wall. * Double accessory duct * Double main pancreatic duct * Tortuous main pancreatic duct